1. Field of the Invention
The present invention relates to a starter for a precombustion chamber type pilot oil ignition gas engine in which a precombustion chamber with liquid fuel injection valve is provided in a cylinder head, and a mixture of air and gaseous fuel that is introduced into a main combustion chamber and compressed is ignited and burnt by pilot oil injected from the liquid fuel injection valve.
2. Description of the Related Art
Conventionally, the engine shown in FIG. 8 is known as a precombustion chamber type pilot oil ignition gas engine that drives a stationary type of power generation installation for industrial or public use.
This type of gas engine 1 has a cylinder liner (cylinder) 2, a piston 3 that moves reciprocally up and down inside the cylinder liner 2, and a precombustion chamber unit 6 with liquid fuel injection valve that is provided with a liquid fuel injection valve 4 and a precombustion chamber 5. Fuel gas (gaseous fuel) such as city gas is mixed with air and is supplied via an intake port of a cylinder head 7 to a main combustion chamber 8 which walls are formed by the cylinder liner 2, the piston 3, and the cylinder head 7. In addition, in the latter half of the compression stroke of the piston 3, fuel oil corresponding to approximately 1% of the total quantity of heat is injected as pilot oil from the liquid fuel injection valve 4 into the precombustion chamber 5. This results in the pilot oil being compression ignited in a high temperature—high pressure atmosphere and the fuel gas inside the main combustion chamber 8 is then burnt using the pilot oil as an ignition source.
A jerk fuel injection pump, which is designed so that a small discharge quantity can be reliably obtained, is used as the fuel injection pump for supplying fuel oil (i.e., pilot oil) to the liquid fuel injection valve 4. Because this jerk fuel injection pump is driven by revolution of the engine via a camshaft, it is affected by an engine speed. In this jerk fuel pump, the relationship between the position of the fuel rack (fuel control rod) which starts fuel injection and the number of engine revolutions (i.e., the engine speed) is shown in FIG. 7. As can be seen in FIG. 7, the smaller the indicated value for the fuel rack position that sets the fuel injection quantity, the wider the range of the engine speed where there is no injection (i.e., the region of the engine revolutions where injection of the fuel oil from the liquid fuel injection valve 4 is not started). For example, if the fuel rack position is set to 8 mm, which is the position corresponding to the discharge quantity of the pilot oil is approximately 1% of the total quantity of heat, the pilot oil is not injected from the liquid fuel injection valve until the engine speed reaches approximately 600 rpm.
Furthermore, in this gas engine 1 the compression ratio is lowered in comparison with a diesel engine in order to avoid knocking during gas operation. Therefore, particularly when the engine is in transition from starting to run-up, if the injection of pilot oil from the liquid fuel injection valve has started, compression ignition of this pilot oil is only achieved with difficulty. In particular, if the engine cooling water is at a low temperature, the compression ignition becomes noticeably more difficult.
Because the gas engine cannot be started in this state, an ignition device 9, such as an ignition plug or a glow plug, is provided in addition to the liquid fuel injection valve 4 so that fuel gas introduced into the main combustion chamber 8 is ignited and the engine is started. However, in this case, because the ignition device 9 is required in addition to the liquid fuel injection valve 4, problems arise in that the engine structure is more complex and costs rise due to the increased number of components.
The present invention was conceived in view of the above circumstances and it is an object thereof to provide a starter for pilot oil ignition gas engine that can reliably inject pilot oil from a liquid fuel injection valve from the time the engine is started, and that can smoothly start the engine.
It is a further object of the present invention to provide a starter for pilot oil ignition gas engine that enables compression ignition to be performed stably using pilot oil when the engine is started even when the engine cooling water is at low temperature.